# 洛谷 [P1337] 平衡点

## 模拟退火练手

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <ctime>
using namespace std;
const int MAXN = 1005;
struct point {
double x, y, wei;
}poor[MAXN];
int n;
const double delta = 0.993;
const double eps = 1e-14;
double xans, yans, ans = 1e15, best = 1e15;
double energy(double x, double y) {
double tot = 0.0;
for(int i = 1; i <= n; i++) {
tot += sqrt((poor[i].x - x) * (poor[i].x - x) + (poor[i].y - y) * (poor[i].y - y)) * poor[i].wei;
}
}
double RAND(double T) {
return (rand() * 2 - RAND_MAX) * T;
}
void solve() {
double T = 10000.0;
best = ans = energy(xans, yans);
double xx = xans, yy = yans;
while(T > eps) {
double xt = xx + RAND(T);
double yt = yy + RAND(T);
double anst = energy(xt, yt);
double DE = ans - anst;
if(DE > 0.0) {
xx = xt; yy = yt;
ans = anst;
if(ans < best) {
xans = xx; yans = yy;
best = ans;
}
} else if(exp(DE / T) * RAND_MAX > (double)rand()) {
xx = xt; yy = yt;ans = anst;
}
T *= delta;
}
}
int main() {
srand(time(NULL));
cin >> n;
for(int i = 1; i <= n; i++) {
cin >> poor[i].x >> poor[i].y >> poor[i].wei;
xans += poor[i].x; yans += poor[i].y;
}
xans /= (double)n; yans /= (double)n;
solve();
solve();
solve();
printf("%.3f %.3f\n", xans, yans);
return 0;
}
posted @ 2018-11-08 14:35  Mr_Wolfram  阅读(145)  评论(1编辑  收藏